1. Field of the Invention
This invention relates to a heat wave shielding lamination, and more particularly to an improved heat wave shielding lamination comprising a plurality of thin layers laminated on the surface of a visible light transparent substrate and possessing excellent shielding effect against heat waves, especially against infrared rays in the vicinity of the visible light range, without impairing the transparency to visible light.
2. Description of the Prior Art
Various plate materials such as those formed of glass or plastic demonstrate good transparency to visible light. However, these same materials also have good transparency to rays beyond the long-wavelength end of the visible light range (infrared rays), and because of this, there are many applications in which it becomes necessary to provide some appropriate means for coping with the energy of the heat waves passing through the plate material. An example of this is seen in the case of car windows which disadvantageously allow sunlight passing therethrough to raise the temperature of the interior of the car, thus making it necessary to equip the car with a large-capacity air conditioner. The need for a heat wave shield is by no means limited to the car window and extends widely to such sheet materials as window panes for air-planes and ships, the lenses of spectacles and cameras, glass panes for buildings and refrigerated showcases, and peephole glasses for such equipment as cooking ovens, furnaces snd welding masks.
There is known a conventional method of providing such a sheet material with a specific coating in order to prevent the passage of heat waves. One known coating material capable of providing some degree of heat shielding is ITO (Indium-Tin-Oxide, which consists of In.sub.2 O.sub.3 with added Sn).
Such conventional coatings are, however, inadequate since they do not provide sufficient heat wave shielding effect and, in particular, since they have low shielding rates against near-infrared rays with wavelengths in the vicinity of 10,000 angstroms which are the rays that it is most important to shut out in shielding against the heat waves in sunlight.
As another means for shielding against heat waves it is known to provide a substrate with a coating which is transparent to visible light and reflects heat waves only. As such coatings there are known, for example, one type consisting of ITO and utilizing the Drude reflection of this substance and another type formed in a multilayer structure and utilizing the interferential reflection effect among the layers. With both of these types there is obtained relatively good reflection of heat waves and a fair degree of heat wave shielding.
The disadvantage of these conventional coatings is, however, that when they are used for high-efficiency reflection of heat waves, they give rise to a secondary problem of heat wave pollution. More specifically, when coatings of this type are used on large-area windows such as the windows of buildings or of automobiles, the heat waves reflected from the coating radiantly heat the surrounding environment thus giving rise to heat wave pollution. Because of this, the range of application of such coatings has been limited.